Disorders of Calcium Homeostasis in Childhood and Adolescence

Calcium is so essential for normal cellular functions that evolution has narrowed the tolerated range for extracellular ionized calcium and developed a complex system to regulate and maintain calcium levels, as well as bone mineralization, with very few redundant mechanisms. Therefore, discovery of hypo/hypercalcemia always reflects a pathological process challenging the fine balance of calcium absorption, PTH secretion and action, vitamin D production and action, cellular compartmentalization of calcium ions, and renal function. In children, normal growth and bone mass accruals require such a large amount of mineral that determinants of blood calcium level are tightly controlled to ensure normal skeletal growth. Indeed, periods of rapid growth are therefore at high risk of hypocalcemia if normal calcium handling is disturbed. Different molecular defects, prolonged severe environmental injuries, or dysregulation of organs and tissues involved in calcium balance, can all result in hypo/hypercalcemia. In this chapter, firstly, we discuss calcium homeostasis and the key hormones of calcium regulation. Then, we talk about the definition, clinical manifestation, and the main causes of hypo/hypercalcemia. Additionally, we propose the initial diagnostic workup and the treatment approach for calcium disorders. Finally, we describe the specific features of underlying diseases of hyper- and hypocalcemia.